Radio transmitter



July 19, 1932.

A. DA. HODGSON RADIO TRANSMITTER Filed July '18, 1951 INVENTOR ALAN D'ARC HODGSON BY (Q T ATTORNEY Patented July 19, 1932 UNITED STATES PATENT OFFICE ALAN DARCY HOIJG'SON, OF SLOUGH, BUCKS, ENGLAND, ASSIGNOR TO RADIO CORPORA- TIQN OF AMERICA, A CORPORATION OF DELAWARE .R-ADIO TRANSMITTER Application filed July 18, 1931, Serial No. 551,641, and. in Great Britain June 6, 1930.

An application for this invention has been filed in England June 6, 1980.

This invention relates to wireless telephony transmitting apparatus, and has for its object to provide means whereby certain of the elements of the apparatus which are normally used for telephony transmission may, when desired, be utilized to cause an audio frequency modulation of the high frequency output, thus enabling the apparatus to be used as a transmitter for interrupted continuous wave telegraphy and the like.

As is known, a simple radio telephony transmitter usually comprises three tubes, one acting as an oscillator, another as a modulator and a third as a speech amplifier for controlling the modulator. The speech amplifier tube generally has its anode connected to the grid of the modulator tube by means of a coupling transformer, and the present invention may be said to relate to apparatus of this kind.

According to the present invention, there is provided in wireless telephony transmit ting apparatus of the kind referred to, in combination with the coupling transformer which connects the anode of the speech amplifier valve to the grid of the modulator tube, a resistance connected across the secondary winding of the transformer, a sliding or like adjustable contact co-operating therewith as in a potentiometer, an electrical connection between said contact and the grid of the speech amplifier tube, a switch in said connection and a Morse key or like current interrupting device in the circuit of the primary winding of said coupling transformer with or without a condenser in the aforesaid electrical connection between the adjustable colraitact and the grid of the speech amplifier tu e.

The accompanyingdrawing illustrates one embodimentof the invention byway of eX- ample.

In this drawing the speech amplifier tube is denoted by the numeral 10, and the modulator tube by the numeral 11. The oscillator tube is not shown but may be of any known type. The anode i of the speech amplifier tube 10 is connected to the grid 6 of the moduformer coupling 12 has connected across it a potentiometer resistance 14 co-operating with a sliding contact 15. The contact 15 is connected by way of a fixed condenser 16 and circuit switch 17 to the grid' 2 of the speech amplifier tube 10.

V The grid of the speech amplifier tube is connected in known manner to one of the terminals of the filament 8 of the speech amplifier tube 10 by means of a high resistance leak 18.

The circuit of the primary winding 9 of the coupling transformer 12 has inserted in it at the low tension side as shown, a Morse key 19.

When the apparatus is to be used as normally for telephony transmission, the switch 17 is open and Morse key 19 permanently depressed. When, on the other hand, the apparatus is to be usedfor interrupted continuous wave transmission, the switch 17 is closed and the Morse key 19 is operated. In this connection, as will be appreciated, when switch 17 is closed, a proportion of the voltage which is generated in the secondary of the coupling transformer 12 leading to the modulator tube is fed back by way of the fixed condenser 16 to the grid of the speech amplifier tube 10. Any oscillation, therefore, such as that which is set up by depressing the Morse key 19 is, transmitted from the speech amplifier vanode 4 to the coupling transformer 12, and

the proportion of voltage referred to is again reflected to the grid 2 of the speech amplifier tube. An audio frequency oscillation is thus set up and is maintained, which is dependent in frequency on the constants of the circuit. By way of further explaining the diagram, 20 is the usual transmitter microphone and 21 the usual coupling transformer by which said microphone is connected to the grid 2 of the speech amplifier tube 10. Also 22 is a grid bias in connection with tube 10.

' It has been found in practice that by the use of the potentiometer 14 and condenser 16 arrangement referred to, not only can the amplitude of the modulated voltage applied *to the modulator grid be varied, but also the V apparatus for radio telephony 'thegrid of the speech amplifier tube is directly connected" toone terminal of the usual microphone trans-,f

former and the circuit through the condenser j i leading to the adjustable contact on the po 1 tentiometer is broken; in other respectsthe frequency of such modulator can be varied over a wide range and a pure modulation tone obtained. When it is desired to use the apparatus can remain fore set forth, 7

connectedas hereinbe- By means of the apparatus described,avery simple, light and easily manipulated arrangement for use in interrupted continuous wave telegraphy and signalling can be provided. 1 Having thus described my invention and the operation thereof, what I claimis 1; In wireless telegraphy or telephony transmitting apparatus including a modu- ,lator, tube having a grid electrode and a speech amplifier tube having an anode and a grid electrode in combination with a coupling transformer having primary and secondary windings which connect the anode of thespeech amplifier tube to the grid of the modulator tube, of a resistance connected across thefsecondarywinding ofthe trans former, an adjustable contact cooperating with said resistance, an electrical connection including a condenser between said contact and the grid of the speech amplifier tube, a switch in said connection and a current interrupting device in the circuitof the primary winding of said coupling transformer.

2. Means for transmitting telegraphy orv v telephony signals comprising a thermionic modulator tube having input electrodes, an I auxiliary tube having input and output electrodes, coupling means including an impedance between the output electrodes of said auxiliary'tube and the input electrodes of 7 said modulator tube, voice frequency responsive means connected with the input electrodes of said auxiliary tube, a resistance connected in parallel with; said impedance, .circuit breaking means connecting said'res'ist'ance to thegrid of said auxiliary tube, Iandjkeying means in the said coupling means.

ALAN DARCY' HODGSON. 

